The invention relates to a method and apparatus for the manufacture of products in the form of controlled uniform size precipitates.
In the manufacture of a number of chemical products, particularly in the pharmaceutical industry, using a precipitation process, it is desired to achieve a high standard of uniformity of particle size in the precipitates and also to control the particle size, generally with the object of achieving a precipitate in the form of uniform small size crystallites. This can be difficult to achieve as crystal growth can occur rapidly and this leads to non-uniformities because of variations in the time periods for which different parts of the precipitate may be exposed to solvent containing unprecipitated solute.
The invention provides, in one of its aspects, a method for the manufacture of a product in the form of a controlled uniform particle size precipitate, which method comprises supplying to a first tangential input of a fluidic vortex mixer a solvent containing the product or a precursor therefor in solution, said fluidic vortex mixer having a second tangential input and an axial outlet, supplying to said second tangential input of the fluidic vortex mixer an anti-solvent, whereby rapid mixing of the solvent and anti-solvent takes place in the vortex mixer and a precipitate of the product or precursor therefor is produced in the solvent/anti-solvent mix emerging from said axial outlet of the vortex mixer, and feeding said emerging mix from the axial outlet directly into a precipitate entrapment device for entrapping the precipitate upon its emergence from said axial outlet for preventing or reducing further growth of said precipitate.
By anti-solvent we mean a fluid which promotes precipitation from the solvent of the product or precursor in solution in the solvent. Anti-solvent may thus have any one of a number of forms depending upon the particular product/precursor, the nature of the solvent and the precipitation process. For example, precipitation from a hot solution can be promoted by cooling, so that the anti-solvent can be a cold fluid. It may comprise the same liquid as the hot solvent or may be a different liquid and, preferably, to provide for continuous re-cycling, is more volatile than the solvent. Or the anti-solvent may comprise a cold gas or a fluid which promotes the precipitation via a chemical reaction or by its effect upon the solubility of the product or precursor in the solvent.
By precipitate entrapment device, we mean any device which will have the effect of so trapping the precipitate as to prevent, or reduce the possibility for, further growth of precipitate particles. For a product which precipitates as crystallites, the entrapment device conveniently comprises a filter medium.
The invention also provides apparatus for the manufacture of a product in the form of a controlled uniform particle size precipitate, which apparatus comprises a fluidic vortex mixer with a first tangential input connected to a source of solvent containing the product or a precursor therefor, and a second tangential input connected to a source of anti-solvent, the fluidic vortex mixer having an axial outlet connected directly into a precipitate entrapment device for entrapping precipitate upon its emergence from the axial outlet for preventing or reducing further growth of the precipitate.
In one arrangement according to the invention the entrapment device is a filter bed which has the effect of rapidly removing precipitate forming in the axial outlet of the vortex mixer from the solvent/anti-solvent mix containing a precipitated product or precursor therefor, and thus preventing or reducing the possibility of further growth of the precipitate.
In such an apparatus there is preferably provided a conduit for conveying the filtrate to a component, such as an evaporator, for concentrating and re-heating the solvent containing unprecipitated product or precursor therefor and separating anti-solvent. Evaporated anti-solvent may be collected and recovered for re-use by condensation and cooling as necessary. Heated solvent containing unprecipitated product or precursor therefor is combined with a product make-up stream for return to the first tangential input of the fluidic vortex mixer in a continuous process.
In certain manufacturing processes, the first stage of precipitation yields an oily phase which is, for example, a metastable form of the final crystalline product. For such processes, the entrapment device conveniently comprises a stirred tank, the oily precipitate emerging from the axial outlet of the fluidic vortex mixer as an emulsion containing small uniform oil particles. These are held in the tank and prevented from coalescing by the stirring for long enough for the oil particles to transform into solid crystallites, after which separation may be effected by, for example, filtration or centrifugation.
Recovered solvent/anti-solvent mix from this separation may be collected and recovered for re-use as described above.